The present invention relates to multiple output switchmode regulated power supplies and more particularly to the process of post regulating at least one power supply output voltage using a switchmode shunt load.
Multiple output regulated switchmode supplies of all types have a common tendency to exhibit poor regulation on outputs that are not sensed. The regulation of these outputs is even poorer when such outputs experience substantially reduced or no-load conditions. Improved or even precise regulation is obtained on such outputs by use of a secondary regulator using a series or pass transistor and a dedicated control loop referenced to a precision reference. The use of a secondary regulator imposes the undesirable burdens of added cost, lower efficiency, size, parts count, weight, cooling requirements, reliability due to increased parts count.
Some multiple output switchmode power supplies sense multiple outputs to obtain improved cross regulation. As one output becomes lightly or heavily loaded its output increases or decreases thereby imposing a cross-regulation decrease or increase penalty on the output voltage of the output operating at constant load. Other multiple output supplies have a xe2x80x9cprimaryxe2x80x9d output voltage that is well regulated and secondary outputs that are xe2x80x9cquasixe2x80x9d regulated, and which may require a minimum load to maintain regulation. The regulated performance of multiple sensed output supplies and xe2x80x9cquasixe2x80x9d regulated supplies, or perhaps even existing xe2x80x9coff-the-shelfxe2x80x9d power supplies may be improved by coupling the invention circuit taught herein to the outputs of such supplies.
An active power supply output bleed balancing circuit is presented that is connected between a first power supply output and a second power supply output while being referenced to a reference potential such as ground. The output bleed balancing circuit improves the regulation of the output voltages of a multiple output switchmode power supply over wide load ranges including a no-load or interrupted load event on one of the output voltages.
The invention circuit functions as an active bleed coupled between the first power supply output and the second power supply output voltages. The circuit is a bi-directional switching regulator programmed to clamp the first power supply output voltage to a value not to exceed the predetermined ration of the second power supply operate at a voltage ratio between input and output. It one output goes too high current is shunted from it to the second output, and vice versa.
The switching topology used for the invention depends on the voltage relationships between Vo1 and Vo2. In general, if Vo1 and Vo2 are both positive, then a buck or boost may be used. If one voltage is negative, a flyback or half wave regulating inverter could be used.